This is a revised R29 application. Streptococcus mutans cariogenicity is associated with its sucrose metabolism via multiple pathways, among which some make sugar polymers for colonization and energy storage, while others produce acid that causes tooth decay. Recent studies have shown that several pathways, ftf; gftBC and scrA, are induced by sucrose, while scrA is repressed by fructose, a product of the Gtf activity. The msm operon is induced intracellularly by fructose, G-1-P and G-6-P, which are sucrose metabolites of various pathways. It is thus hypothesized that S. mutans shows coordinated expression of several sucrose pathways. The coordinated expression may be mediated by sucrose metabolites, such as fructose or G-1 -P, which may be generated from one pathway and cross- regulate another. When sugar is unavailable, polysaccharide-degradation pathways may be induced in response to sugar starvation to release free sugars, which in turn may cross-regulate other pathways. To date, 13 sucrose metabolic pathways of S. mutans have been identified. Among them, nine major pathways have been genetically studied: these are gtfB, gtfC, gtfD, ftf; dexA, fru, scrAB, msm and glg; the remaining four are the trehalose, glucose and fructose PTS pathways and the glycogen degradation pathway. Since the genes and mutants of the nine major pathways are available, we can begin testing this hypothesis immediately. We propose to: (1) Identify cross-regulation of other pathways on msm, dexA or fruA, which can be monitored directly by chromogenic chemicals, using isogeneic mutants. (2) Identify cross-regulation of other pathways on ftf, gtfBC, scrA and glg, which do not have a readily assayable phenotype, using strains in which one pathway is fused with a reporter gene and the other is inactivated. (3) Evaluate cross-regulation simultaneously among multiple pathways. (4) Identify induction of polysaccharidedegradation pathways in response to sugar starvation. The results will help us understand the genetic regulation of S. mutans sucrose metabolism, which is critical for S. mutans virulence.